Locomotor-respiratory coupling represents motor coordination between locomotion and breathing. This coordination is essential for sustained locomotion in many vertebrates including mammals and represents a form of entrainment, in which the two rhythmic activities with different frequencies become phase-locked due to mechanical and neural interactions. Using an isolated neonatal rat brainstem-spinal cord preparation, we have previously reported that spinal locomotor generators exert a remote control of brainstem respiratory neural network (Le Gal et al. (2014) PLoS ONE) and may take an active part in the increased respiratory rhythmicity produced at the onset and during episodes of locomotion in mammals.

Didier Morin de l'INCIA: Here, we show that the locomotor-related signal produced by the lumbar central pattern generator for locomotion is also able to selectively modulate the intracellular activity of spinal respiratory neurons engaged in expiration (see illustration, part A). We therefore report in spinal cord the existence of thoraco-lumbar bimodal neurons with the ability to display a spontaneous expiratory activity pattern (see illustration, part B upper trace) and a clear locomotor-related behavior (part B lower trace).

Consequently in freely-moving animals, the influence of the lumbar locomotor generator on expiratory neurons that control ventral trunk musculature could produce spine bending during locomotion and facilitate respiratory exhalation. Finally, our results contribute to our understanding of the cellular bases for coordinating the rhythmic neural circuitry responsible for different behaviors.